This invention relates to a semiconductor sensor, and more particularly to a semiconductor acceleration sensor.
As an example of prior art semiconductor sensors, an accelerometer is discussed at pp. 1911-1917 of IEEE Transactions on Electron Devices, Vol. ED-26, No, 12, December, 1979. This accelerometer is basically structured by the step of etching a silicon substrate to create a rectangular silicon supporting rim in which a mass or weight is supported by an extremely thin silicon beam. The beam is provided with a resistor. The stress induced in the beam by vibration of the mass is detected electrically in terms of changes in the resistance values of resistors. In such a semiconductor accelerometer, the detection sensitivity of acceleration is proportionate to the weight of the mass. As the substrate is made of silicon single crystal of &lt;100&gt; orientation, and the mass element is fabricated by anisotropic etching, there is formed between the mass element and the surroundings an interstice in the form of a V-shaped groove at an angle of 54.7.degree.. The width of the groove inevitably becomes as wide as the thickness of the substrate to thereby pose a problem in minimizing sizes. If the size of the accelerometer is to be reduced, the size of the mass which occupies the central portion should be reduced, but when the width of the mass is reduced close to the thickness of the wafer, it is inconveniently etched laterally in the case where a single crystal &lt;100&gt; silicon is used as the substrate. Therefore, the mass element cannot be fabricated precisely to the design dimensions by the anisotropic etching. The conventional method is defective in that when the structure is reduced in dimension, the weight of the mass which is greatly influential to determination of frequency characteristic of such semiconductor accelerometer cannot be set with a high precision. Further, even if the mass is formed in a size allowing reasonably good etching, it still is impossible to form a mass having an arbitrary weight within a space limited by a supporting rim which provides a cantilever. In order to form the mass with a weight sufficient to allow detection of acceleration, there is no alternative but to enlarge the outer circumferences of the supporting rim. It was heretofore extremely difficult to minimize the size of such accelerometer.
This limitation of the prior art is not limited to semiconductor accelerometers alone, but is shared by dynamic sensors such as a semiconductor dynamic sensor, a pressure sensor, etc. A physical quantity (such as temperature or light) can be detected by transducing them it into a mechanical quantity applied on a weight or a beam and reading it with a semiconductor sensor. Such sensors, however, are not free of the above defects.